Disc drive memory systems have realized intensified demands because of new environments for usage, miniaturization and increased performance needs. Besides traditional computing environments, including PCs, network servers and workstations, disc drive memory systems are currently used by devices including digital cameras, digital video recorders, laser printers, photo copiers, jukeboxes, video games and personal music players.
Disc drive memory systems store digital information that is recorded on concentric tracks of a magnetic disc medium. Several discs are rotatably mounted on a spindle, and the information, which can be stored in the form of magnetic transitions within the discs, is accessed using read/write heads or transducers. A drive controller is conventionally used for controlling the disc drive system based on commands received from a host system. The drive controller controls the disc drive to store and retrieve information from the magnetic discs. The read/write heads are located on a pivoting arm that moves radially over the surface of the disc. The discs are rotated at high speeds during operation using an electric motor located inside a hub or below the discs. Magnets on the hub interact with a stator to cause rotation of the hub relative to the shaft. One type of motor is known as an in-hub or in-spindle motor, which typically has a spindle mounted by means of a bearing system to a motor shaft disposed in the center of the hub. The bearings permit rotational movement between the shaft and the hub, while maintaining alignment of the spindle to the shaft.
Demands of the market and advances in technology have lead to the reduction in the physical size of disc drives. Efforts have been made to design smaller profile disc drives without loss of performance. The one-inch disc drive currently on the market includes a CF card type II with a 5 millimeter (mm) thickness. A demand exists for smaller mobile applications, and it has become essential in the industry to design disc drives having even smaller dimensions while maintaining motor stiffness. For example, a CF card type I form factor requires a disc drive having a 3.3 mm thickness but such disc drive is not yet on the market.
The demand for increased storage capacity and smaller disc drives has led to the design of higher recording area density such that the read/write heads are placed increasingly closer to the disc surface. Misalignment and mispositioning between data tracks and the read/write transducer can limit the data track density and overall performance of the disc drive system. Accurate positioning of the data head over a storage track on the disc is therefore of great importance in writing data to the disc and reading data from the disc. In current disc drive products, a commonly used type of actuator is a rotary moving coil actuator. The discs themselves are typically mounted in a stack on the hub structure of a brushless DC spindle motor. The rotational speed of the spindle motor is precisely controlled by motor drive circuitry which controls both the timing and the power of commutation signals directed to the stator windings of the motor. The hub includes a sleeve or back iron portion which carries a magnet. The stator is affixed to the base plate. Interaction between the magnet and the stator causes controlled rotation of the hub about the shaft.
Disc drive performance is related to the degree of alignment between the stator and the magnet (and therefore alignment of the stator and base plate), both axially along the axis of rotation and radially. Alignment of the magnet and stator, and alignment of the stator and base plate, in both the axial and radial direction is expensive and difficult during volume production of disc drive motors due to tolerances incurred in producing the magnet, stator and base plate parts.
Base plate materials currently utilized for a one-inch disc drive include aluminum and steel. In manufacturing a base plate for a disc drive having a thin dimension, aluminum base casting becomes ever more difficult and it has become a trend to utilize a stamping technology to reduce manufacturing costs. Additionally, as disc drives are designed with thin dimensions, base plate stiffness is a concern and materials other than aluminum possess greater stiffness. To maintain stiffness with thin dimension disc drives, a steel material such as stainless steel or cold rolled steel is typically utilized for the stamped base plate.
While a number of features of a steel base are stamped, further machining is necessary for the base and stator interface to obtain acceptable alignment. However, accurately machining a properly aligned base plate and stator interface is problematic, in part due to the small dimensions. Further, added difficulties arise in machining a stamped steel base including increased cutter wear and a longer process cycle time, as compared to machining an aluminum base. Additionally, the base plate stator interface requires further inspection after machining. Accordingly, there is a need for consistent alignment of a stator with a base plate such that motor performance is maintained and precise interface machining is unnecessary, for use with a hard disc drive having thin dimensions that meets stiffness requirements.